The present invention relates generally to organic acid corrosion inhibitors for antifreeze compositions. More particularly, the present invention relates to mixtures comprising a carboxylic acid, or salt, isomer or mixture thereof, and a cyclohexenoic acid, or salt, isomer or mixture thereof, for use in antifreeze compositions as corrosion inhibitors to provide prolonged corrosion protection to the aluminum metal surfaces in cooling and/or heating systems, such as those found in internal combustion engines.
Corrosion has long been a problem when certain metals or alloys are used in applications in which they come into contact with an aqueous medium. For example, in heat-transfer systems, such as those found in internal combustion engines, alcohol-based heat transfer fluids (i.e., antifreezes) can be very corrosive to the metal surfaces of the heat-transfer systems. Compounding this problem is the fact that the corrosion is accelerated under normal engine operating conditions (i.e., high temperatures and pressures).
Aluminum surfaces, are particularly susceptible to corrosion. See Darden et al., xe2x80x9cMonobasic/Diacid Combination as Corrosion Inhibitors in Antifreeze Formulations,xe2x80x9d Worldwide Trends in Engine Coolants, Cooling System Materials and Testing, SAE Int""l SP-811, Paper #900804, pp. 135-51 (1990) (xe2x80x9cSAE SP-811xe2x80x9d).
Indeed, aluminum surfaces are susceptible to several types of corrosion including general corrosion, pitting and crevice corrosion as well as cavitation-erosion corrosion. These types of corrosion, however, typically occur under different conditions and thus, affect different types of aluminum surfaces. For example, general corrosion usually occurs on aluminum surfaces which are readily susceptible to corrosion because they are poorly inhibited or because they are subject to xe2x80x9cheat-rejectingxe2x80x9d conditions (e.g., cylinder heads) or xe2x80x9cheat-acceptingxe2x80x9d conditions (e.g., radiators and heater cores).
Pitting/crevice corrosion usually occurs on the thin aluminum sheets used in radiators or heater cores. Such corrosion generally results from localized penetration of the oxide film which would otherwise cover and protect the aluminum surfaces. See SAE SP-811.
Cavitation-erosion corrosion (xe2x80x9cCE-typexe2x80x9d corrosion), like pitting/crevice corrosion, attacks the protective oxide film which can result from implosion of bubbles on the aluminum surfaces. See SAE SP-811 at p. 136. CE-type corrosion can be accelerated by the formation of foam in the cooling system. Foam results from air bubbles which are entrapped and agitated in the cooling system. See, e.g., Nalco, xe2x80x9cCooling System Liner/Water Pump Pitting,xe2x80x9d Technifax TF-159 (1988). Thus, aluminum water pumps, which are used to circulate antifreeze coolants throughout a vehicle""s cooling and/or heating systems, are particularly susceptible to CE-type corrosion. This is so because bubbles are readily formed on the trailing sides of the water pump impeller blades due to locally reduced pressure and consequent boiling caused by the high rotation rate. When these bubbles collapse in higher pressure areas in the water pump, they can erode the metal in these areas. This process can eventually destroy the impeller causing loss of pumping performance and/or can perforate the pump body leading to loss of engine coolant. See, e.g., Oakes, xe2x80x9cObservation on Aluminum Water Pump Cavitation Tests,xe2x80x9d Second Symposium on Engine Coolants, ASTM STP 887, pp. 231-48 (1986).
The corrosion of aluminum surfaces has become a significant concern in the automotive industry because of the increasing use of such lightweight materials. See, e.g., Ward""s Auto World, p. 22 (September, 1996); Ward""s 1996 Automotive Yearbook, p. 27 (58th ed. 1996). For example, heat exchangers in cars and light duty trucks are now being constructed using aluminum components including the water pumps. See Hudgens et al., xe2x80x9cTest Methods for the Development of Supplemental Additives for Heavy-Duty Diesel Engine Coolants,xe2x80x9d Engine Coolant Testing: Second Volume, ASTM STP 887, Beal, Ed., ASTM, Philadelphia, 1986, pp. 189-215; Oakes xe2x80x9cObservations on Aluminum Water Pump Cavitation Tests,xe2x80x9d Engine Coolant Testing: Second Volume, ASTM STP 887, Beal, Ed., ASTM, Philadelphia, 1986, pp. 231-248; Beynon et al., xe2x80x9cCooling System Corrosion in Relation to Design and Materials,xe2x80x9d Engine Coolant Testing: State of the Art, ASTM STP 705, Ailor, Ed., ASTM, Philadelphia, 1980, pp. 310-326. In particular, CE-type corrosion has become a significant concern because, aside from mechanical seal failures caused by high thermal stresses and inadequate lubrication, CE-type corrosion is one of the leading causes of water pump failures. See, e.g., Beynon, supra at pp. 310-326 (1980).
In general, corrosion inhibitors have been used to protect the metal surfaces used in heat transfer systems. For example, triazoles, thiazoles, borates, silicates, phosphates, benzoates, nitrates, nitrites and molybdates have been used in antifreeze formulations. See, e.g., U.S. Pat. No. 4,873,011; see also, SAE SP-811 at pp. 135-138, 145-46. However, such corrosion inhibitors have several problems, including expense, and inadequate long-term protection. See U.S. Pat. No. 4,946,616, col. 1, lines 31-45; U.S. Pat. No. 4,588,513, col. 1, lines 55-64; SAE SP-811, pp. 137-38. Accordingly, automobile manufacturers have begun using, and several now require, organic acid based (or extended life) corrosion inhibitors such as mono- and/or di-carboxylic acids. A number of carboxylic acid corrosion inhibitors have been described. See, e.g., U.S. Pat. Nos. 4,382,008, 4,448,702 and 4,946,616; see also U.S. Pat. No. 5,741,436, incorporated herein by reference.
However, carboxylic acid corrosion inhibitors, while effective at protecting against general and pitting/crevice types of aluminum corrosion, are generally ineffective as CE-type corrosion inhibitors. See, e.g., D. E. Turcotte, xe2x80x9cEngine Coolant Technology, Performance and Life for Light Duty Application,xe2x80x9d Fourth Symposium on Engine Coolants (1997). Indeed, many of the known aluminum corrosion inhibitors, while effective at protecting against one or more types of aluminum corrosion, are generally not known to be effective at inhibiting all types of aluminum corrosion. For example, silicates and phosphate salts known to be effective at inhibiting general corrosion and CE-type corrosion, are not known to inhibit pitting/crevice corrosion. Also, nitrates which are known to be effective pitting/crevice corrosion inhibitors, are not known to inhibit general or CE-type corrosion. Certain carboxylic acid based compositions comprising polymerizable-acid graft polymers useful as cavitation-erosion corrosion inhibitors are also disclosed in co-pending U.S. patent application Ser. No. 08/999,098, filed Dec. 29, 1997, and incorporated by reference herein.
Certain cyclohexenoic acids are known and used primarily in the preparation of water-soluble surfactants. See, e.g., U.S. Pat. Nos. 3,931,029 and 4,476,055. Other cyclohexenoic acids have been used as corrosion inhibitors in metal working applications and as corrosion inhibitors in antifreeze compositions for inhibiting the corrosion of metals other than aluminum (e.g., solder alloys). See, e.g., U.S. Pat. No. 3,931,029. However, such corrosion inhibitors were not known to be effective as aluminum corrosion inhibitors and in particular, CE-type corrosion inhibitors.
Thus, there remains a need for a composition which provides improved CE-type corrosion inhibition of aluminum surfaces and which provides acceptable overall corrosion inhibition of aluminum surfaces.
The present invention provides antifreeze concentrates comprising:
(a) from about 90% to about 99.89% by weight of a liquid alcohol which functions as a freezing point depressant, or mixture thereof;
(b) from about 0.1% to about 5.5% by weight of a carboxylic acid selected from the group consisting of saturated and unsaturated aliphatic, and aromatic, mono-, di- and tri-carboxylic acids, and salts and isomers thereof, and any mixture thereof; and
(c) from about 0.01% to about 2% by weight of a cyclohexenoic acid, or salt, isomer or mixture thereof, having the formula: 
wherein each of R1, R2 and R3 is independently selected from the group consisting of H, OH, COOH, C1-C10 alkyl groups, glycol esters, or combinations thereof
The inventive concentrates have been found to be surprisingly effective exhibiting reduced corrosion of aluminum surfaces, especially CE-type corrosion. The present invention also provides antifreeze formulations comprising the inventive concentrates and methods of inhibiting such corrosion using the inventive concentrates.
In order that this invention may be more fully understood, the following detailed description is set forth.
The present invention provides antifreeze compositions which demonstrate surprisingly increased inhibition of aluminum surfaces and in particular, increased inhibition of CE-type corrosion of aluminum surfaces. Antifreeze compositions refer to antifreeze concentrates and antifreeze formulations which comprise a concentrate diluted with water.
The inventive antifreeze concentrates comprise:
(a) from about 90% to about 99.89% by weight of a liquid alcohol which functions as a freezing point depressant, or mixture thereof;
(b) from about 0.1% to about 5.5% by weight of a carboxylic acid selected from the group consisting of saturated and unsaturated aliphatic, and aromatic, mono-, di- and tri-carboxylic acids, and salts and isomers thereof, and any mixture thereof; and
(c) from about 0.01% to about 2% by weight of a cyclohexenoic acid, or salt, isomer or mixture thereof, having the formula: 
wherein each of R1, R2 and R3 is independently selected from the group consisting of H, OH, COOH, C1-C10 alkyl groups, glycol esters, or combinations thereof.
Suitable liquid alcohols which function as freezing point depressants include any alcohol or other heat transfer medium and preferably is at least one alcohol, selected from the group consisting of methanol, ethanol, propanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, glycerol, the monoethylether of glycerol, the dimethylether of glycerol, alkoxy alkanols (such as methoxyethanol) and mixtures thereof The preferred alcohol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol and mixtures thereof.
The liquid alcohol component is added in the amount of from about 90% to about 99.89% by weight of the concentrate.
The carboxylic acid used in the antifreeze composition herein described may be selected from the group consisting of saturated and unsaturated aliphatic and aromatic mono-, di- and tri-carboxylic acids, and inorganic and organic salts (e.g., alkali and alkaline earth metal, ammonium and amine salts) and isomers thereof and any combination thereof. Preferred carboxylic acids include C4-C12 mono- or di-carboxylic acids such as 2-ethyl hexanoic acid, neodecanoic acid, neodecanoic acid, benzoic acid, t-butylbenzoic acid, dodecanedioic acid and sebacic acid, or salts (e.g., alkali and alkaline earth metal, ammonium or amine salts), isomers or mixtures thereof More preferred carboxylic acids include C8 mono-carboxylic acids (e.g., 2-ethyl hexanoic acid) as well as mixtures having a major amount of a C8 mono-carboxylic acid component (e.g., neo-octanoic acid and/or 2-ethyl hexanoic acid, more preferably 2-ethyl hexanoic acid) and neodecanoic acid, or salts (e.g., alkali and alkaline earth metal, ammonium or amine salts) or isomers thereof. Where the mixture of a C8 mono-carboxylic acid component and neodecanoic acid is used, the preferred mixture comprises the C8 mono-carboxylic acid component and neodecanoic acid in the weight ratio of about 3:1 See U.S. Pat. No. 5,741,436, incorporated herein by reference.
The carboxylic acid component is added in an amount of from about 0.1% to about 5.5% by weight of the concentrate, preferably from about 1% to about 5%, and more preferably from about 2% to about 4% by weight.
The cyclohexenoic acid component has the structure: 
wherein each of R1, R2 and R3 is, independently, selected from the group consisting of H, OH, COOH, C1-C10 alkyl groups, glycol esters, or combinations thereof Where the substituents comprise a C1-C10 alkyl group, more preferred alkyl groups have up to six carbon atoms because such groups are believed to result in cyclohexenoic acids having improved miscibility in the antifreeze composition.
For the cyclohexenoic acid component, R1 is preferably H or COOH (with COOH more preferred), R3 preferably comprises a C1-C10 alkyl group, and R2 preferably has the structure:
xe2x80x83(CH2)xxe2x80x94(COO)xe2x80x94[(CH2)yxe2x80x94O]zxe2x80x94H
wherein:
x is from 0 to 10;
y is from 1 to 5; and
z is from0to 5.
Preferably, z is 0-2, more preferably z is 1 or 2, and even more preferably z is 2. Examples of useful cyclohexenoic acids include: 
The cyclohexenoic acid component is added in an amount of from about 0.01% to about 2.0% by weight of the concentrate. The only expected constraint is the miscibility of the cyclohexenoic acid (or its salt) component in the concentrate. Preferably, the cyclohexenoic acid component is added in an amount 15 of from about 0.01% to about 1.0%, more preferably from about 0.1% to about 1.0%, and even more preferably from about 0.1% to about 0.3% by weight of the concentrate.
The cyclohexenoic acids used in this invention, including those specifically described above, may be obtained from Westvaco Corporation.
The acid components of the antifreeze compositions of this invention may alternatively be in the form of an alkali metal salt, ammonium salt or amine salt. Preferred salts are the alkali metal salts, and most preferred are sodium or potassium salts of the acids.
The antifreeze compositions may also include one or more additional corrosion inhibitors, such as triazoles, thiazoles, phosphates, borates, silicates, molybdates, nitrates, nitrites or the alkali metal, alkaline earth metal, ammonium or amine salts thereof In some applications, for example heavy duty engine applications, the antifreeze compositions of this invention further comprise nitrite. Preferably, the antifreeze compositions of this invention further comprise a triazole or thiazole, more preferably, an aromatic triazole or thiazole such as benzotriazole (xe2x80x9cBZTxe2x80x9d), mercaptobenzothiazole (xe2x80x9cMBTxe2x80x9d) or tolyltriazole (xe2x80x9cTTZxe2x80x9d) and most preferably, TTZ. Such additional corrosion inhibitors may be added in concentrations of up to about 5.5% (by weight of the antifreeze composition).
The antifreeze composition may also comprise a sufficient amount of an alkali metal hydroxide to adjust the pH to between about 6.0 to about 11.0, preferably to about 6.5 to about 9.0. Other additives may also be used depending on the application. Suitable additives include dyes (e.g., xe2x80x9cAlizarine Green,xe2x80x9d xe2x80x9cUranine Yellowxe2x80x9d or xe2x80x9cGreen AGS-liquidxe2x80x9d from Abbey Color Inc., xe2x80x9cOrange II (Acid Orange 7)xe2x80x9d or xe2x80x9cIntracid Rhodamine WT (Acid Red 388)xe2x80x9d from Crompton and Knowles Corp.), odor masking aids, perfumes, bitterants, antifoams, rust inhibitors, pH buffers, scale inhibitors, and/or sequestration and dispersion agents (e.g., xe2x80x9cDequestxe2x80x9d from Monsanto Chemical Company, xe2x80x9cBayhibitxe2x80x9d from Miles Inc., xe2x80x9cRejext-itxe2x80x9d from PMC Specialties Group, xe2x80x9cNalcoxe2x80x9d or xe2x80x9cNalPREPxe2x80x9d from Nalco Chemical Company).
The antifreeze concentrates of the present invention can be used to prepare antifreeze formulations. To form such an antifreeze formulation, the concentrate is diluted with water. Preferably, the antifreeze formulation comprises from about 10% to about 90% by weight water, and more preferably from about 25% to about 75% by weight water.
It will be appreciated by one of skill in the art that the amounts of the components of the antifreeze compositions may vary when minor adjustments are made to the other components of the compositions.
The present invention also provides methods for inhibiting corrosion of the aluminum components in internal combustion engines. Such methods comprise the step of contacting the aluminum components to be protected with the antifreeze compositions described above.
In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and are not to be construed as limiting the scope of the invention in any way.